Automatic electric toaster



Nov. 18, 1947. o v c; I 2,431,195

AUTOMATIC ELECTRI C TOASTER File,d Oct. 9, 1944 I5 Sheets-Sheet 1 9 Fig-J INVENTOR. i2? J E/vol? 6104mm Nov. 18, 1947; B. G. OLVING AUTOMATIC ELECTRIC TOA-SIER 3 Sheets-Sheet 2 Filed Oct. 9, 1944 4 IN VEN TQR. BROH Q. 04 w/va Nov. 18, 1947.

B. G. OLVING 2,431,195

AUTOMATIC ELECTRIC TOASTER Filed Oct. 9, 1944 3 Sheets-Sheet 5 INVEN TOR. BROR Q01 w/va Patented Nov. 18, 1947 AUTOMATIC ELECTRIC TOASTER Bror G. Olving, Elgin, Ill., assignor to McGraw Electric Company, Elgln, 111., a corporation of Delaware Application October 9, 1944, Serial No. 557,900

7 Claims.

My invention relates to automatic electric toasters, and particularly to means for timing the duration of a toasting operation.

An object of my invention is to provide a timing means and an electric circuit therefor, which are dependable and will stand up for long periods of service.

Another object of my invention is to provide a timing means, the performance of which depends upon the inherent electrical characteristics of its component parts and the operation of which is not dependent on or controlled by energy supplied from mechanical or thermal storage devices,

Another object of my invention is to provide an electric timing means and an electric circuit therefor, including an electron tube, to obtain the above mentioned performance.

Another object of my invention is to provide a timing circuit, including an electron tube and means for varying the duration of a toasting operation to compensate for temperature changes of the toaster structure, different circuit voltages, and to permit of obtainin different degrees of toasting desired by the user.

In the drawings,

Figure 1 is a view, in side elevation, of a toaster, having operatively associated therewith a system embodying my invention,

Fig. 2 is a front view of the toaster, Figs. 1 and 2 being on a reduced scale.

Fig. 3 is a vertical, sectional view through a toaster having associated therewith a timing ircuit embodying my invention,

Fig. 4 is a vertical, lateral, sectional view therethrough, taken on the line 44 of Fig. 3,

Fig. 5 is a fragmentary, horizontal, sectional View, taken on the line 5-5 of Fig. 4,

Fig. 6 is a diagram of connections embodying my invention, and,

Fig. '7 is another diagram of connections embodying my invention.

Referring first to Figs. 1 to 5 inclusive, I have there illustrated a standard automatic two-slice electric toaster, designated generally by the numeral 2| and comprising a bottom frame member 23, which may be made of pressed composite material and which supports at its upper end a bottom plate 25 and an outer casing 21 thereon.

The casing is provided with an inter-fitting cover member 29, and I have elected to show a twoslice toaster such as is now on the market.

I provide two pairs of vertical, planar heatin elements designated generally by the numeral 3|,

.each of said heating elements comprising one or more sheets 33 of electric-insulating material,

' such as mica, on which is wound a strip 35 of a front intermediate wall 4|.

tions of carriers 45 are secured to a rear car-- suitable resistance material. planar heating elements 3! is positioned in a toasting chamber, of which one of said elements constitutes one side, while a baffle plate 31 constitutes the other side. An intermediate rear wall 39 and a front intermediate wall 4| are also provided, and these walls and baflle plates are supported and held in desired proper operative positions by any means now well known in the art. I provide also a. plurality of vertically extending guard and guide wires 43, which are also supported in any manner now well known in the art and serve to prevent lateral movement of a slice of bread being toasted in a toasting chamber and engagement thereof with the resistor 35.

I provide also a pair of bread carriers 45, one in each of the toasting chambers, the rear end portions of which extend through vertical slots in the rear intermediatewall 39, while the front end portions extend through vertical slots in the The front end porriage plate 41, which is of substantially rectangular shape and has rotatably mounted thereon four grooved rollers 49 at or adjacent to the respective corners thereof. A front carriage plate 5i isalso provided, and the rollers are positioned between the front and the, rear carriage plates. The pairs of rollers are adapted to engage vertical standards or rods 53 and .55, the lower ends of which are fixedly secured in plate 25, while the upper ends are secured in the front end portions of top frame plates 51 extending from front to rear above the respective toasting chambers.

The front portions of the frame plates 51 are secured together by a cross bar 59. A tension coil spring 6| has its upper end secured to a small bracket 63- mounted on front intermediate wall 4|, while its lower end is secured to a rearwardly extending lug 65 forming a part of the rear carriage plate 41. Spring 6| biases the bread carriers into their upper ornon-toasting position, from which they may be moved by any suitable means into their lowered or toasting positions shown by the broken lines in Fig. 3.

The front carriage plate 5| has mounted thereon a forwardly extending bar 61 which projects outwardly through a vertical slot in the front wall of the outer casing 21 and has an actuating knob 69 mounted thereon, by means of which an operator can move the carriers downwardly against the tension of the biasing spring 6| until the carriers are positioned in their lowermost or Each pair of the or stub shaft 19 pivotally supported as by a bracket 80 below the bottom plate 25. Energization of the toast heating elements 3I is controlled by a resilient contact bridging member 8| insulatedly supported by the front carriage plate I. A pair of fixed contacts 83 and 85 are supported on a block 91 of electric-insulating material which is supported by a bracket 39 from the front intermediate wall 4I. When the carriers are moved into their lowermost or toasting position, contact bridging member BI will engage the two fixed contacts 33 and 35 to cause energization of the four electric toast heating elements.

I provide also an additional pair of contact members 9I and 93 which are supported on a block 95 of electric-insulating material which is supported by a bracket 91 secured to the front intermediate wall 4| adjacent to the upper end portion thereof, so that they will be engaged by contact bridging member 8| when it has been moved together with the carriers into the upper non-toasting positions of the latter. The purpose of these two upper additional contacts will hereinafter appear.

While I have illustrated and described in Figs. 1 to 5 inclusive specific embodiments of a standard domestic type of automatic electric toaster, I do not desire to be limited thereto, since all of these elements are old and well known in the art and constitute no part of my present invention, which will now be described.

Referring now to Fig. 6 of the drawings, I have there shown a circuit embodying my invention and including an electron tube IN. This tube includes a heating filament I03 which is adapted to be energized by a small resistor I05 connected in series with one supply circuit conductor I01 and the toast heating elements 3|. The tube IOI includes an indirectly heated cathode III, a plate or anode II3, as well as a grid H5, and a screen grid II1. Electron tubes of this type and kind are well known in the art.

The inner terminal of the small resistor I05 is connected to one terminal of the toast heating elements 3 I, while the other terminal of the other toast heating element 3I is connected by a conductor II9 to the lower fixed contact 83. The other fixed contact 85 is connected by a conductor I2I to the other supply circuit conductor I09, the two supply circuit conductors being adapted to :be connected to an alternating current source of supply. A half wave dry type rectifier I23 has one of its terminals connected to conductor II9, while its other terminal is connected by a conductor I25 with one terminal of a resistor I21, the other terminal of which is connected to one terminal of a potentiometer I29, the other .terminal of which is connected by a conductor I3I to one terminal of a small resistor I33, the other terminal of which is connected to a conductor I35. Conductor I35 has one end connected to a conductor I31 extending from one terminal of resistor I05 to one terminal of the heating filament I03, while the other end thereof is connected to screen grid II1.

Resistor I33 is a grid bias resistor. Resistor I21 has a zero temperature coeflicient 01 resistance, that is its resistance does not change appreciably with change of temperature and is preferably located in the bottom portion of the toaster, so that its ohmic resistance, which may be on the order of 3000 ohms, will not change appreciably. The ohmic resistance of the potentiometer I29 when cold, may be on the order of 300 ohms and that of the grid bias resistor I33 may be 100 ohms.

A filter condenser I39 has one terminal thereof connected to a tap on resistor I21, while its other terminal is connected to conductor I31. The capacitance of the filter condenser I39 may be on the order of one-half microfarad. The minor portion of resistor I21, the ohmic resistance of which may be on the order of 100 ohms, serves the purpose of limiting the filter condenser charging current through rectifier I23 to a safe value at the instant of closing the main switch, including the contacts 33 and and bridging member 8|. The filter or ballast condenser I33 serves the purpose of smoothing out the ripples of the rectified voltage wave and of absorbing random surges of the voltage supply in order to improve the accuracy and reliability of the timing operation. The potentiometer I29 has a manually-adjustable contact arm I4I, the fixed terminal of which is connected by a conductor I43 to one terminal of a timing resistor I45, the other terminal of which is connected to one terminal of a timing condenser I41, the other terminal of which is connected to conductor I3I. The junction of the timing resistor I45 and of the timing condenser I41 is connected to one terminal of a resistor I49, the other terminal of which is connected to grid H5. The resistor I49 has a value on the order of 25,000 ohms in order to limit the discharging current of the condenser I41 through the tube IN, and the capacitance of condenser I41 may be on the order of 5 microfarads.

As has already been hereinbefore stated, when the carriers are moved downwardly into toasting position, hook member 1I will engage member 13 of a latch, which includes a magnetizable armature core I5I adapted-to be energized by a coil I53. One terminal of coil I53 is connected by a conductor I55' to conductor I25, while the other terminal of coil I53 is connected by a conductor I-51 with anode II3 of tube IOI. The ohmic resistance of the timing resistor I45 is on the order of 10 megohms. The magnitude of the charging voltage to the timing circuit comprising the timing resistor I45 and the timing condenser I41 and therefore the length of time required to charge the timing condenser I41 to its firing" potential is dependent upon the portion of potentiometer I29 connected in circuit by contact arm I connected to timing resistor I45, and also upon its temperature. Upon energization of the circuit at the start of a toasting operation the rectified half waves of direct current potential provided by rectifier I23 will be applied to condenser I41 through the timing resistor I45, and the action of charging the condenser I41 is analogous to the charging of a secondary or storage battery, that is the potential at the terminal of condenser I41 will be increased gradually and, when starting with a cold toaster, it will require a length of time on the order of two and one-half to three minutes until the potential across the terminals of condenser I41 has reached a value sufficient to fire the tube IOI or to make the initially nonconductive tube become conducting. Thi voltage of the timing condenser I41 necessary to fire the tube IOI may be on the order of 25 volts. The

circuit traversed by the current traversing tube I M may be traced as follows: from supply circuit conductor I09 through conductor I2I to the main heater control switch, including contacts 85 and 83 and bridging member 8|, through a conductor I I9, through rectifier I23, through conductors I25 and I55, coil I53, through conductor I51, through tube I M, and from there through conductor I3I, resistor I33, and conductors I35 and I31 to the second supply circuit conductor I01. The energized coil I53 causes quick upward movement of core I5I with resultant disengagement of latch member from hook member H and quick upward movement of the bread carriers into non-toasting position with attendant engagement of bridging member 8I with the upper fixed contacts 9| and 93.

The bridging member 9|, which is in engagement with the upper fixed contacts 9| and 93 during non-operating positions of the parts of the toaster, provides a discharge circuit for condenser I41 as follows: contact 9| is connected to conductor II9 by a conductor I59, while contact 93 is connected by a conductor I60 to the junction of terminals of the timing resistor I45 and of the timing condenser I41. The circuit through which condenser I41 discharges is substantially as follows: from the upper terminal of condenser I41 through conductor I 60 to contact 93, through bridging member 8| to contact member 9|, conductor I59 and conductor II9, through toast heating elements 3|, through resistor I05, conductor I31, a part of conductor I35, through grid bias resistor I33, and then through conductor I3I to the other terminal of condenser I41.

Theresistor of potentiometer I 29 has a positive temperature coefficient of resistance, so that upon quickly successive toasting operations, the temperature increase of potentiometer I29 will cause an increase in the value of the ohmic resistance, so that, with a fixedposition-of contact arm I4I, the voltage applied to the condenser I41 will increase, with the result that the charging of condenser I41 to a firing voltage is reduced, so that substantially the same degree of toasting will be obtained, irrespective of the temperature of the toaster structure. It is only necessary to properly correlate the cold resistance of the potentiometer I29, that of the timing resistor I45, as Well as the coefficient of resistance of potentiometer I29, to obtain the desired result of substantially the same degree of toasting of successive slices of bread, irrespective of variations of the temperature of the toaster.

In order to obtain different degrees of toasting of successive slices of bread, it is only necessary to manually adjust the position of contact arm I4I of the potentiometer I29 in order to vary the degree of toasting, from light, to medium, or to dark. If contact arm MI is moved in a counterclockwise direction, the potential impressed upon the timing condenser I41 through the timing resistor I45 will be decreased, and therefore the duration of a toasting operation will be increased, with the result that instead of light toast, medium toast, or even dark toast will be obtained.

Referring now to Fig. 7 of the drawings, I have there shown another circuit which is adapted to be energized from a direct current source of supply. A gas triode tube I6I has a heating filament I83 which is adapted to be connected to and energized by a small resistor I05. An indirectly heated cathode I55 is part of tube I5I, which includes also a grid I01 and a plate anode I59. I provide a pair of supply circuit conductors HI and I13, of which In is connected to resistor I05, the other terminal thereof being connected to toast heating elements 3|. The other terminal of toast heating elements 3| is connected by conductor I I9 to terminal 83 of the main switch and by conductor I15 to one terminal of coil I53 of the electromagnetic latch release means. The other terminal of coil I53 is connected by conductor I11 to one terminal I19 of a second or auxiliary electromagnetic relay. The second fixed contact terminal I8I of this relay is connected to conductor I 31. A contact bridging member I83 is supported by an armature core I85, which is adapted to be energized by a coil I81. One terminal of coil I81 is connected by a conductor I89 to conductor I15 and therefore to contact 83, while the other terminal of coil I81 is connected by a conductor I9I to plate anode I provide a potentiometer I29, one terminal of which is connected to conductor I31. while the other terminal thereof is connected to a resistance I93, the other terminal of which is connected by a conductor I to conductor H9. The value of the ohmic resistance of potentiometer I29, when cold, is on the order of 2000 ohms. The resistor material of potentiometer I29 has a positive temperature coefficient of resistance and it is subject to heat from the toast heating elements. The coefficient of resistance of potentiometer I29 is such that its resistance, when hot, is on the order of 5000 ohms. The ohmic resistance of resistor I93, which has a substantially zero temperature coefficient of resistance is on the order of 8000 ohms.

The potentiometer I29 has a manually-adjustable contact arm I4I, which is connected by a conductor I43 with a timing resistor I45, the ohmic value of the resistance thereof being on the order of 10 megohms. One terminal of resistor I45 is connected to one terminal of a timing condenser I41, which has a capacitance on the order of 5 microfarads, the other terminal thereof ,being connected to conductor I31. The junction of one terminal of timing resistor I45 and of the timing condenser I41 is connected to one terminal of a resistor I49, the ohmic value whereof is on the order of 50,000 ohms. Resistor I49 serves to limit the discharge current from condenser I41.

Let it now be assumed that a user desires to toast one or two slices of bread, starting with a cold toaster. After putting in the slice or slices of bread, he will press down on knob 69 to move the carriers into toasting position, so that hook 1I will engage with the hook 15 on the latch to hold the carriers in toasting position, as well as to hold the contact bridging member 8| in engagement with fixed contacts 83 and 85. Charging of the condenser I41 (Fig. 7) will begin through potentiometer I29 and particularly that part thereof included in the circuit by the contact arm I4I, the rest of the circuit being constituted by conductor I43, timing resistor I45 and the timing condenser I41, through conductor I31, and from there to the other terminal of potentiometer I29. The value of the ohmic resistance of this charging circuit is such that the time required to charge condenser I 41 to a potential which will fire tube IliI, will require a length of time on the order of two and one-half to three minutes, de-

pending of course upon the degree of toasting desired. When condenser I41 has been charged to a potential which will cause firing of tube I8I, this potential being on the order of 15 volts, the tube will become conducting, with the result of current flowing through the tube through a circuit traceable as follows: from supply circuit conductor I13 through conductor I2I, through the closed main switch comprising contacts 85, 83, and bridging member 8|, through conductor I89, coil I81, conductor I9I, tube IBI to cathode I85, and from there through conductor'I31 to the other supply circuit conductor I1I. This causes energizing of coil I81, with the result of causing engagement of contact bridging member I83 with fixed contacts I19 and IBI, whereby an energizing circuit is closed through coil I53 of the main or latch releasing means, traceable as follows: from supply circuit conductor I13 through conductor I2 I, through closed main switch comprising contacts 85, 83 and bridging member 8|, through conductor I15, coil I53, through conductor I11, the engaged contacts I19 and I8| with contact bridging member I83, and from there through conductor I31 to the second supply circuit conductor I1I. The energized coil I53 causes raising of the core I5I and attendant release of hook member H from book 15 and quick upward movement of the bread carriers into non-toasting position.

'3I, then through resistor I05 and through conductor I31 to the other terminal of condenser I41. The fully discharged condenser will therefore start any succeeding operation in substantially the same initial condition as it did for the first operation.

The subjection of the potentiometer I29 to heat from the toast heating elements serves also as a means for compensating for temperature increase of the toaster structure, which temperature increase causes a greater amount of toasting to take effect in a given length of time. The resistance of that part of potentiometer I29 connected in the charging circuit increases with increase of temperature of potentiometer I29, so that a higher potential is impressed upon the timing resistor I45 and on condenser I41, with the result that a shorter period of time is required to charge condenser I41 to a potential equal to that necessary to fire the tube I6 I. Proper correlation of the resistance of the charging circuit and of the potentiometer will ensure that the desired correlation of the length of time of a toasting operation with the desired degree of toasting will be obtained.

By use of the manually-adjustable contact arm I of the potentiometer I29, it is possible to preset the timing circuit to obtain any desired degree of toasting during a toasting operation. Thus if contact arm I4I is turned in a counter-clockwise direction, the charging potential applied to condenser I41 through resistor I45 will be reduced so that it will require a relatively longer time to charge condenser I41 to a potential at which tube ISI will be fired. Conversely, if contact arm I is turned in a clockwise direction, the potential applied to condenser I41 through resistor I45 is increased so that the degree or toasting obtained will be lessened because it will require a shorter time to charge condenser I41 to its firing potential.

It is evident therefore that in each of the two timing circuits illustrated in Figs. 6 and 7, I have provided an electron tube having an indirectly heated cathode, one of these tubes being adapted for use on an A. C. circuit, while the other is adapted for use on a D. C. circuit, the normally non-conducting tube being rendered conducting by a timing condenser charged from the supply circuit through a potentiometer having a positive temperature coefiicient of resistance and being therefore inherently capable of varying the duration of a toasting operation in accordance with the temperature of the toaster structure, making it shorter with increase of temperature of the toaster structure, and making it longer with decrease of temperature of the structure. The manually-adjustable contact arm also provides a means for presetting the degree of toasting which will be obtained from a toasting operation, irrespective of the temperature of the toasting structure.

Various modifications may be made without departing from the spirit and scope of my invention,

and all such modifications clearly coming within the scope of the appended claims shall be considered a part of my invention.

I claim as my invention:

1. In an automatic electric'toaster, the combination with a toasting chamber, toast heating elements in said chamber and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, a timing resistor and a timing condenser adapted to be energized from said potentiometer to cause increase ofthe potential of said condenser, an electron tube connected to said condenser and adapted to be fired thereby when the potential of said condenser has reached a predetermined value, means energized by' the current traversing the tube for terminating a toasting operation, said potentiometer being positioned to receive heat from the heating elements and having a positive temperature coefficient of resistance to cause substantially uniform toasting of successive slices of bread, irrespective of changes or temperature of the toaster and means for causing discharge of the condenser through the toast heating elements at the termination of a toasting operation.

2. In an automatic electric toaster, the combination with a toasting chamber, toast heating elements in said chamber and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, a timing resistor and a timing condenser adapted to be energized from said potentiometer to cause increase of the potential of said condenser, an electron tube connected to said condenser and adapted to be fired thereby when the potential of said condenser has reached a predetermined value, means energized by the current traversing the tube for terminating a toasting operation, said potentiometer being positioned to receive heat from the heating elements and having a positive temperature coefllcient of resistance to cause substantially uniform toasting of successive slices of bread, irrespective of changes of temperature of the toaster and being also manually-adjustable to preset the degree of toasting obtained during a toasting operation and means for causing discharge of the condenser through the toast heat- 9 ing elements at the termination of a toasting operation.

3. In an automatic electric toaster, the combination with a toasting chamber, toast heating elements in said chamber and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, a timing resistor having a positive temperature coefiicient of resistance, located close to the toasting chamber and a timing condenser adapted to be energized from said potentiometer to cause increase of potential of .said condenser, an electron tube connected to said condenser and adapted to be fired thereby, means energized by the current traversing the tube for terminating a toasting operation, said potentiometer being manually-adjustable to preset the duration of a toasting operation to obtain a predetermined degree of toasting during said toasting operation and means for causing discharge of the condenser through the toast heating elements at the termination of a toasting operation. K

4. In an automatic electric toaster, the combination with a toasting chamber, electric toast heating elements in said chamber, a control switch for said heating elements biased to open position and including a contact bridging member, means to move the switch to closed position to start a toasting operation and a releasable latch to hold said switch in closed position, of means for effecting release of said switch to terminate a toasting operation, comprising a potentiometer subject to heat from said heating elements, a timing resistor and a timing condenser connected to be energized by said potentiometer to increase the potential of said condenser, a hot cathode electron tube connected to said condenser and adapted to be fired thereby at a predetermined voltage, means energized by the current traverslng the tube to cause release of the latch and termination of a toasting operation, said potentiometer having a positive temperature coefficient of resistance to cause substantially uniform toasting of successive slices of bread, irrespective of temperature variations in the toaster and means for causing discharge of the timing condenser through the toast heating elements at the termination of a toasting operation.

5. A toaster as set forth in claim 4 in which said potentiometer is manually-adjustable to preset the duration of a toasting operation to thereby predetermine the degree of toasting of a slice of bread. 1,

6. In an automatic electric toaster, the combination with a toasting chamber, electric toast heating elements in said chamber, a control switch for said heating elements normally biased to open position and including a contact bridging member, a bread carrier in said toasting chamber movable into toasting and non-toasting positions relatively to said heating elements and biasedto non-toasting position, means to move the switch gized by the current traversing the tube to cause release of the latch and termination of a toasting operation, said potentiometer having a positive temperature coefiicient of resistance to cause substantially uniform toasting of successive slices of bread, irrespective of temperature variations in the toaster and means including said contact bridging member for causing discharge of the timing condenser through the toast heating ele-' ments at the termination of a toasting operation. 7. A toaster as set forth in claim 6 in which said potentiometer is manually-adjustable to preset the duration of a toasting operation to thereby predetermine the degree of toasting of a slice of bread.

BROR, G. OLVING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,363,169 Fischer Nov. 21, 1944 2,182,124 Guerra Dec. 5, 1939 2,061,011 Vingerhoets Nov. 17, 1936 2,207,871 Myers July 16, 1940 2,215,404 Myers Sept. 17, 1940 2,317,228 Shroyer Apr. 20,1943 2,364,998

Palmer et al Dec. 12, 1944 

